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In western NA there are at least 5 different species in that group, known as Sect. Colymbadini. Four of them we have in California. One is provisionally named as C. flavobasalis or flavobasilis.. It occurs in California and I have one collection from Ron and a couple from mine. It is widespread in Western NA, but in California I have seen it only up North, down to the central Sierra near Trucky.

We have 3 new species in that group, which so far appear limited to California, but this is likely because we have done most sequencing of that group here in the state.

Cortinarius ahsii is a real species that occurs in the Western NA and the Rockies, but so far has not been collected in California. Luckily, now we know exactly what C. ahsii is as the type was sequenced. What we thought to be C. ahsii, Ron, is very, very close, but different (one of ther 3 new species in Cal.).

As far as this collection here, it is hard to say what it is, but if I had to vote I’d go for C. flavobasilis.

The yellow veil is not really a veil, but yellowish remnants around the lower stem, which may glow under UV, but this reaction is not guaranteed. In general, based on at least 50 collections, I have found that particular feature to be unreliable. One can learn to id to that group easily with a little bit of experience, which is best done in the field. I believe that potentially one can even become decent in identifying these to species in the field, but in general I believe that this group is challenging enough that I am not aware of anyone who has it pinned down reliably yet. Molecular data solves a lot of the problems… but we will have to learn the phonotypical expression on the basis of that.